Electronic toll collection systems (“ETC”) are commonly used to facilitate the collection of a toll from a moving vehicle traveling on a toll roadway.
Automatic Vehicle Identification (“AVI”) is the process of determining the identity of a vehicle on the roadway. Typically, electronic toll systems use a series of antennas that are mounted near the roadway which provide coverage areas that extend the width of a lane. Radio frequency (“RF”) transponders are mounted on or within a vehicle to communicate with the antennas. A roadside AVI reader typically interrogates the transponder using the antenna. Typically the roadside reader is connected to a vehicle detector and imaging system which permits vehicles to be detected, classified, and photographed, and the license plate numbers analyzed in order to permit the operator of the toll system to apply appropriate charges to the owner of the vehicle.
After the AVI reader has read the data transmitted by the transponder, the reader typically transmits updated information to the transponder using at least one of the antennas. For example, the reader may transmit a record of the plaza and lane for subsequent retrieval at a later toll plaza, or it may transmit information to control audio and visual displays associated with the transponder. The AVI reader also typically re-interrogates the transponder to ensure the updated information has been programmed.
In some circumstances, a transmission problem may occur resulting in a failed programming attempt. For example, the transponder or the AVI reader may not receive a signal if the transponder has traveled outside of the coverage area of the antenna used to transmit the programming signal. Interference caused by other electrical devices may also result in the programming signal or a portion of the programming signal not being received by the transponder. A transmission error may also occur due to reflections, multipath and the attenuation of the RF programming signal as it passes from the exterior of the vehicle to the interior of the vehicle where the transponder is typically located.
It is therefore desirable to provide an improved communication system and method for communicating with a transponder located in a moving vehicle in a toll roadway.